[fireflies_]

But all the prior blocks are static, that's the point. If you can break the cipher used at some time t, anything that people had "stored securely" by encrypting it and putting it on the blockchain before time t is vulnerable. As our technology and understanding gets better, t might get later and later. Obviously it depends on your use case, but it's a good argument for not putting sensitive things out in public on a blockchain at all.